Turbine and compressor blades



Feb. 21, 1961 N. H. KENT TURBINE! AND COMPRESSOR BLADES Filed Feb. 11,1958 2 Sheets-Sheet 1 FIG.2.

PIC-3.38.

F' I (5.3A.

INVE NTOR ATTORNEYS Feb. 21, 1961 N. H. KENT 2,972,182

TURBINE AND COMPRESSOR BLADES Filed Feb. 11, 1958 2 Sheets-Sheet 2Neesorz, lNVENTO R ATTORN EYS 2,972,182 Patented Feb. 21, 1951 &5

2,972,182 TURBINE AND COMPRESSOR BLADES Nelson Hector Kent, Allestree,Derby, England, assignor to Roll's-Royce Limited, Derby, England, aBritish company Filed Feb. 11, 1958, Ser. No. 714,654

Claimspriority, application Great Britain Feb. 22, 1957 I 6 Claims. (CI.291'56.8)

invention relates to the manufacture of blades and particularly turbineand compressor blades for internal combustion turbine engines forexample from metals which are resistant to high temperature such asnickelchrome alloys.

Such blades may have passageways running axially of the blade for theflow of cooling or heating fluid such as air.

It has hitherto been proposed to form a blade of said type by a processincluding the following steps:

I (a) producing a billet,

(b) drilling a plurality of holes axially of the billet, the crosssection of such holes being circular, and i (c) extruding the billet ina die with lubrication thereby to produce a blade section of approximateaerodynamic form, said holes being thereby deformed to be ofsubstantially oval, elliptical or lenticular form, the major axes ofwhich lie on or approximately parallel to the camber line of the blade.

According to the present invention the process of forming a blade in themanner described above is modified by drilling the holes to be of oval,elliptical or lenticular cross-section by an electrical drillingprocess, the extrusion of the billet being such as to extend the majoraxes of said holes and to decrease the minor axes thereof.

The adoption of the present invention enables blades to be producedhaving cooling passages with very high axis ratio.

In using the term axially we include holes which will eventually runthrough the blade spanwise and which may be inclined to the true axis ofthe blade and therefore initially of the billet. Thus for example incertain blade designs it may be desirable for the holes at the leadingand trailing edges to be slightly so inclined to accommodate thenarrowing of the blade toward the tip.

Electrical drilling processes used for the manufacture of blades inaccordance with the present invention may include processes involvingthe removal of metal by electric spark action, by electric anodic actionor by electric arc erosion or disintegration, such methods permittingthe drilling of holes of oval, elliptical or lenticular form.

The billet may be initially of substantially rectangular cross-section,in which case deformation during the extrusion will take placesubstantially wholly between the two opposite faces of the rectangularsection.

Preferably the holes are blind holes so that in the final extrusionthese holes terminate adjacent the portion of the extrusion which ismachined to form the root-fixing portion of the blade. Suitable holesmay then be drilled in the root-fixing portion to connect with the holesin the profile portion of the blade which lead out through the tipshroud or platform.

The holes may be filled with a filler material prior to being extruded.

Preferably a split die is used for the extrusion which will facilitatethe extrusion by pressure in a single sense. Filler material used in themanufacture of blades according to the present invention may be of lowcarbon steel and the filler material may be removed by dilute nitricacid to which a wetting agent has been added. A particularly suitablelubrication for the billet during extrusion may be obtained bynickel-plating the billet and applying a colloidal graphite to theextrusion die surface, as described in co-pending US. application SerialNo. 702, 519 filed December 13, 1957, now Patent No. 2,947,076.

Platform portions may be formed at the tip and root portions of theblade either from material which is subsequently welded to or from metalleft on the blade portion after extrusion or partly by one method andpartly by the other. For this purpose the billet may be only partiallyextruded-that is to say a part of it will not be deformed in theextrusion process.

An example of this invention will be described by reference to theaccompanying drawings.

Figure l is an elevation of a blade which may be manufactured by theprocess of the present invention.

Figure 1A is a view of the same blade in the direction at right anglesto that of Figure 1.

Figure 2 is a vertical section through the billet from which the bladeis to be extruded after the blind holes have been drilled.

Figure 2A is a section on the line IIA-IIA of Figure 2.

Figure 3 is an end view of one-half of the extrusion die.

Figure 3A shows the same one-half of the die in plan.

Figure 3B is a section through the two halves of the die on a plane atright angles to the two die faces.

Figure 4 is an elevation of the billet after extrusion.

Figure 4A is a section on the line IVA-IVA of Figure 4.

Figure 5 is a section on the line VV of Figure 4 after the blade profileportion has been twisted.

Figures 6 and 6A are diagrams showing the eifect on the drilled holes ofthe method of extrusion according to this invention.

Figure 7 shows a method of drilling the holes.

The billet 10 is formed from a cut bar by forging. Oval or ellipticalblind holes 11 are then drilled in it by the electric arc drillingprocess described in co-pending US. application Serial No. 697,456 filedNovember 19, 1957 and illustrated in Figure 7. Rods of low carbon steel,e.g. of mild steel having a carbon content of less than 0.25% areinserted in the holes and are located by welding at the ends of theholes. The billet is then nickelplated to provide lubrication duringextrusion and then heated and extruded in a split die, the two halves ofwhich are shown at 12 and 13. In order to improve the lubrication duringextrusion it has been found desirable to apply graphite to the surfacesof the extrusion die. During extrusion the reduction of cross-sectionalarea takes place substantially Wholly at right angles to the plane ofthe die split.

On removal from the die the billet has the shape shown in Figures 4 and4A. The effect of the extrusion is to deform oval holes 11 into theshape shown in Figure 6A as a result of the extrusion pressure exertedin the direction of the arrow shown in Figure 6.

It will be appreciated that by initially drilling the holes to beelliptical and subsequently extruding the billet according to the methodof this invention it is possible to produce blades with coolingpassageways having a very high axis ratio.

The billet on removal from the die has a blade portion 14 and anon-extruded portion 15 from which an integral tip shroud will bemachined.

The next step is to twist the blade portion 14 whereby a section as atVV of Figure 4 occupies the position shown in Figure 5 relative to thenon-extruded portion of the billet 15.

Referring to Figures 1 and 1A it will be observed that the root-fixingportion of the blade comprises fir-tree fixing 20, a stem portion 21 andrudimentary platform portions 22. These parts are provided by thematerial at the tip 14a of the extruded section shown in Figure 4. Holes24 are drilled through the 'fir-tree root 2'0 and stem portion 21 toconnect with the flattened holes 1} in the blade profile portion.

From the unextruded portion 15 at the blade tip a tip platform 19 may bemachined by means of a suitable cam profiling machining in known manner.

The filler material may be removed from the holes 11 at any time afterextrusion and dilute nitric acid with a wetting agent added may be usedfor this purpose. 7

The initial drilling of the holes may be as described in co-pendingU.S.application Serial No. 697,456 and illustrated in Figure 7.

The billet 18 is mounted in a carrier 22 which is caused gradually totravel downwards by a shaft 23 to which the carrier is bolted and whichhas a rack engaged by a pinion 25 carried by a shaft 26 supported inbearings from fixed structure 27 by a casing 28. Shaft 26 carries on oneend a pinion 29 which is driven by a pinion 30 from an electric motor31, the speed of which is controlled by a speed control 32. On the otherend of shaft 26 is a pulley 33 carrying a weight 34 which helps to holdthe billet steady. The electric motor drive causes the billet to descendat the rate of 0.02 to 0.08 inch per minute. An extension upward ofshaft 23 slides through a bearing 35 supported from the fixed structure27 and guides the shaft 23 vertically. V

A hollow tubular drill 35 is carried by a shaft 37 in a bearing 38 fromthe fixed structure. The drill is further supported by a series ofX-shaped rods 39 from an upright cylinder 40 to which they are locatedby nuts 41. The rods at their point of intersection carry ring bearings40a which support slidably the drill. The rods can be removed in turn asthe drill passes further into the hole which it is forming in thebillet. A sodium silicate solution of say one part of silicate to threeparts of water or other suitable electrolyte solution is fed bycompressed air from a tank 42 through pipe 43 to the hollow interior ofshaft 37 whence it passes up through the hol low drill washing away thedisintegrated debris and cooling the drill and billet at the point ofdisintegration. Thereafter it flows down between the drill and the wallsof the hole to insulate the drill from the billet, the liquid passesfrom the cylinder 40 through escape pipe 45. The insulation of the sidefaces of the drill from the billet material is further increased by theformation of an anodic film which is not broken down by thereciprocation of the drill. At the bottom of shaft 37 an eccentric orcrank 46 driven from a motor 47 through belt 48 causes the shaft 37 tobe reciprocated or vibrated at a frequency from 3000 to 4000 cycles perminute.

A direct current or an alternating current superposed on a directcurrent is passed from lead 49 and drill 36 across the arc gap betweendrill and billet through the billet holder 22 and lead 50. Satisfactorydrilling has V 4 been obtained using a voltage of between 6 and 24giving rise to a maximum current of the order of amps.

I claim:

1. The method of forming from a metal which is resistant to hightemperatures and for an internal combustion turbine engine a blade ofthe type which has cooling passages running axially thereof, includingthe following steps:

(a) producing a billet of said metal of roughly rectangular crosssection having a major axis of the order of the finished width of theblade and a minor axis substantially greater than the finished thicknessof the blade at its thickest point;

(b) drilling axially of the billet by an electric drill ing process aplurality of holes of generally elliptical cross section, having theirmajor axes oriented generally the same as the major axis of the billet;

(c) filling each drilled hole with a close fitting filler of malleablemetal capable of selectivedissolution for removal; 7' H (d) extrudingthe billet axially of the holes in .a die with lubrication to produce ablade section of approximately aerodynamic form by exerting extrudingpressure in a direction to increase the major axes and decrease theminor axes of said drilled holes so that they become lenticular and aroot section; Y

(e) machining the blade profile and then removing said filler.

2. The method claimed in claim 1 in which extrusion is carried out in asplit die.

3. The method claimed in claim 1 in which the drilled holes are blindand in which registering holes are drilled through the rootportion ofthe billet after extrusion.

4. The method claimed in claim 3 in which part only of the billet isextruded including the blind portion and an integral tip shroud ismachined from the non-extruded portion. 7

5. The method claimed in claim 4 in which the nonextruded portion of thebillet terminates in an. inclined surface at its end adjacent theextruded portion.

6. The method claimed in claim 4 in which a root fixing portion isformed from the tip of the extruded portion of the billet.

References Cited in the file of this patent UNITED STATES PATENTS2,013,622 1 Bedford et a1. Sept. 3, 1935 2,047,555 Gardner July 14, 19362,628,417 Peyches Feb. 17, 1953 2,751,988 Lemont et al. June 26, 1956,830,357 Tunstall et al Apr. 15, 1958 2,836,884 Graham Iune 3 i958FOREIGN PATENTS 745,655 Great Britain Feb. 29, 1956 755,610 GreatBritain Aug. 22, 1956 763,141 Great Britain a; Dec. 5,1956

